For the past several years, experts have noticed that the condition of many relatively new buildings has deteriorated markedly. Several causes have been cited:
1. While other buildings were often constructed in a massive mode, for esthetic reasons and to keep costs low less massive structures have been preferred in constructing newer buildings.
2. Not only changing weather conditions (temperature, sunlight, moisture), but also to an increasing extent chemical influences (deicing salt, carbon dioxide, nitrogen oxides, sulfur dioxide) contribute toward a rapid deterioration of conventional building materials. The combination of physical changes and chemical attack results in carbonatization of concrete, in elimination of passivation and formation of metal rust, and in peeling off of a structure's facing.
3. At the same time, physical stresses increase, e.g., bridges carry an increased volume of traffic including heavy freight carrying trucks.
Rarely is the tearing down and complete rebuilding of damaged structure economically justified. Obviously, the better approach is to preserve and restore. There is a need for better procedures, and more particularly better materials making it more feasible to effect restoration. Epoxy resin-cement mortars, chemically compatible with steel and concrete, are especially well suited for this purpose.
A plastic-containing binder is disclosed, for example, in DAS No. 1,198,267, consisting of a hydraulic cement, water, an epoxy resin curable at normal temperature, and a curing agent. Preparation of this binder is cumbersome since two premixes must be produced separately from each other and may be combined only immediately prior to use. The relatively brief processing time of about 1-2 hours is the basic drawback not only in using this system but also in all so-called 2K systems (see, for example, DOS No. 2,840,874). After each use, all processing equipment which has been in contact with the binder, must be thoroughly cleaned to avoid clogging and the formation of difficult to remove deposits.
U.S. Pat. No. 3,926,886 relates to a 1K epoxy resin-diammonium acetate or formate emulsion consisting of a liquid epoxy resin, water and a substituted diammonium salt, with curing taking place in the presence of cement. The diammonium salt performs a dual function: after reaction with the alkaline-acting cement, the less basic diamine is liberated (a) curing the epoxy resin and (b) serving as an emulsifier. However, the resultant emulsion may not be stable, especially if the work is to be conducted under extreme weather conditions. Accordingly, the patentees propose to add up to 15% of a commercial emulsifier to the mixture being emulsified. Even so, stability of the emulsion is not certain.
In EP-Al-00 43 463, acid is added to keep the amine component from reacting with the epoxy resins at elevated temperature; any adducts formed are rendered water-soluble and dispersible by addition of the acid. In the present invention, the goal is to prepare an emulsion from a diammonium salt and an epoxy resin wherein the curing process is initiated at temperatures of above 0.degree. C. only upon addition of an alkaline-reacting compound.
The patent literature describes numerous emulsifiers suitable for use in conjunction with aqueous epoxy resin dispersions:
U.S. Pat. No. 3,879,324:
Surface-active compounds, such as anionic and cationic compounds.
Canadian Pat. No. 879,750:
Mixtures of nonylphenoxypoly(ethoxy).sub.19 ethanol and alkylene oxide extended alkyl phenol polyglycol ethers.
German Pat. No. 2,800,323:
Poly(ethylene oxide) esters of fatty acids.
DAS No. 1,669,772:
Addition products of 25-30 moles of alkylene oxide and abietic acid.
U.S. Pat. No. 3,020,250:
Synthetic compounds, proteins.
DOS No. 1,925,941:
Amine-epoxy resin condensation products.
DAS No. 2,332,165:
Mixtures of abietic acid polyglycol esters, polyglycol ethers of fatty acids and/or polyglycol ethers of p-alkyl phenol and long-chain aliphatic alcohols of 8-18 carbon atoms.
East German Pat. No. 135,915 describes 2K dispersions containing a polysulfide, a polyepoxide, and a polyvinyl alcohol, utilized as coating agents or as cement additives. Building materials containing organically bound sulfur are not in general use since it can accelerate the corrosion of steel.
More recently, formulations were developed superior to those described in U.S. Pat. No. 3,926,886 with regard to availability of the amine component, stability of the emulsion and spectrum of usage. German Patent Application No. P 32 22 531.8, corresponding to U.S. Pat. No. 4,442,245, teaches emulsions consisting of an epoxy resin, a primary aliphatic C.sub.12-14 -alcohol and/or its adduct with ethylene oxide groups, water, and the salt of an alkylene diamine and oxalic acid. In German Patent Application No. P 32 22 528.8, corresponding to U.S. Pat. No. 4,440,882, the salt of a polyamine or a polyaminoamide with oxalic acid is utilized as the latent curing agent.
Notwithstanding these improvements, stability of the emulsion remains uncertain. Problems occur, particularly, if the epoxy resin itself is not readily emulsifiable in water. Also, the formation of air pores due to entrained air has an adverse effect when such emulsions are used to produce mortars.
Although it is known that it is possible to improve the flexibility of concretes by means of certain polymer additives (European Laid-Open Application No. 0 055 035), it is likewise known that concretes containing polyvinyl acetate have not proven themselves under practical conditions. This is due to the fact that, under the influence of moisture, the polyvinyl acetate is saponified forming polyvinyl alcohol. At the same time, the technical properties of the concrete are impaired (see DOS No. 31 36 737).